The present invention concerns boilers for generating steam and removing solids from high temperature, solids-containing gaseous effluents.
Steam is the foremost vehicle for power generation in the world. About 90% of the new electric capacity being installed utilizes steam. In the eighteenth century, a "shell" boiler, little more than a ketttle filled with water and heated at the bottom, was the most common source of industrial steam. This, in turn, was followed by early versions of the "fire-tube" boiler such as the Trevithick boiler. John Stevens, a lawyer instrumental in the passage of this nation's first patent act, patented a "water-tube" boiler in 1803.
Steam was originally utilized to provide heat and power for local industrial use. With the advent of practical electrical power generation and distribution, utility companies were formed to serve both residential and commercial users. By 1881 the first electric generating station in the United States utilizing steam was operating in Philadelphia.
Modern boilers are generally of the "water-tube" type. In this type of boiler, the water and steam are inside the tubes and the hot gases generated by the combustion of fuel such as natural gas, oil or coal, are in contact with the outer tube surfaces.
A less common type of boiler is the "fire-tube" boiler. In this boiler, the hot gaseous products of combustion pass directly through the tubes. The tubes are surrounded by water contained in a vessel. "Fire-tube" boilers are designed for vertical, inclined or horizontal positions. The preferred position being horizontal.
"Fire-tube" boilers represent only a small fraction of the steam generating devices presently in use. Many of the "fire-tube" boilers currently in service are used for heating small buildings. The demise of "fire-tube" boilers in larger sizes for process steam generation is a result of their large volume of water compared to their heating surfaces. Thus in case of mechanical failure due to tube burnout there can be an explosive release of a large quantity of steam.